In the 1930s, the Mountaineers, a Seattle-based hiking, climbing and conservation organization, came up with a list of 10 essential items no climber/hiker should be without. Experience rescuing others taught them that if hikers would simply carry these 10 essentials, they would be able to survive backcountry emergencies until help arrived.
The 10 Essentials should be carried by every hiker at all times:
Navigation: map, altimeter, compass, GPS device, PLB, satellite communicator or satellite phone, extra batteries or battery pack
Headlamp/flashlight: plus extra batteries
Sun protection: hat, sunglasses, sun-protective clothes, lip balm and sunscreen
First aid: including foot care and insect repellent (if required)
Knife: plus repair kit
Fire: matches, lighter and tinder, or stove as appropriate
Shelter: carried at all times (can be a lightweight emergency bivvy)
Extra food: beyond minimum expectation
Extra water: beyond minimum expectation, or the means to purify
Extra clothes: sufficient to survive an emergency overnight
The extra essentials
Toilet paper (hygiene kit)
Whistle — signal an emergency by blowing your whistle in series of threes
As time passes, new technology (GPS, cell phones, etc.) have redefined what items people consider essential. The original 10 Essentials are still the best presentation of the base items every hiker should carry.